This application relates, inter alia, to novel aqueous oral care compositions useful for combining and delivering poorly compatible ingredients, for example to deliver effective levels of cationic antibacterial agents in combination with polyphosphate salts that protect against erosion and staining.
Biofilms form when bacteria adhere to surfaces in some form of watery environment and begin to excrete a slimy, glue-like substance that can stick to all kinds of materials—metals, plastics, soil particles, medical implant materials, biological tissues. Dental plaque is a biofilm that adheres to tooth and other oral surfaces, particularly at the gingival margin, and is implicated in the occurrence of gingivitis, periodontitis, caries and other forms of periodontal disease. Dental plaque is cohesive and highly resistant to removal from teeth and/or oral surfaces. Bacteria associated with dental plaque convert sugar to glucans, which are insoluble polysaccharides that provide plaque with its cohesive properties. Anaerobic bacteria in plaque metabolize sugar to produce acids which dissolve tooth minerals, damaging the enamel and eventually forming dental caries. Saliva can buffer acids produced by bacteria and promote remineralization of the enamel, but extensive plaque can block the saliva from contact with the enamel. Redeposition of minerals in the biofilm forms a hard deposit on the tooth called calculus (or tartar), which becomes a local irritant for the gums, causing gingivitis.
Various antibacterial agents can retard the growth of bacteria and thus reduce the formation of biofilm on oral surfaces. In many cases, these antibacterial agents are cationic, for example quaternary ammonium surfactants such as cetyl pyridinium chloride (CPC), bisguanides such as chlorhexidine, metal cations such as zinc or stannous ions, and guanidines such as arginine.
Everyday activities such as smoking or other oral use of tobacco products, and eating, chewing or drinking certain foods and beverages (particularly coffee, tea, cola drinks, and red wine), cause undesirable staining of surfaces of teeth. Staining can also result from microbial activity, including that associated with dental plaque. The chromogens or color causing substances in these materials become part of the pellicle layer and can permeate the enamel layer. Even with regular brushing and flossing, years of chromogen accumulation can impart noticeable tooth discoloration.
A tooth is comprised of an inner dentin layer and an outer hard enamel layer that is the protective layer of the tooth. The enamel layer of a tooth is naturally opaque, and white or a slightly off-white color. The enamel layer is composed of hydroxyapatite mineral crystals that create a somewhat porous surface. These hydroxyapatite crystals form microscopic hexagonal rods or prisms that make up the enamel surface. As a result, the surface of the enamel presents microscopic spaces or pores between the prisms. Without limiting the mechanism, function, or utility of the present disclosure, it is believed that this porous nature of the enamel is where discoloring substances permeate the enamel and discolor the teeth.
Since the compounds that stain the teeth are typically anionic materials, cationic antibacterial agents can cause or enhance staining by facilitating the deposit of chromogens or by forming salts with minerals.
One approach to reducing staining and erosion as well as reducing biofilm formation is the use of a dentifrice, such as a mouthwash, containing mineral agents useful in stain removal. Polyphosphate salts, for example, exhibit significant stain fighting ability, and when used in oral care products, they deposit onto and protect the tooth surface, as well as complexing with free calcium, thereby starving bacteria and reducing calculus deposition. However, when phosphates are combined with cationic antibacterial agents, particularly in high water formulations where the two can readily interact in solution, the phosphates and the cationic antibacterial agents can complex to form insoluble precipitates, thereby inactivating both components.
There is thus a need for novel oral compositions and methods that inhibit staining and biofilm formation, and in particular that can provide both the anti-staining and anti-calculus benefits of phosphates and also the anti-bacterial and anti-biofilm benefits of a cationic antibacterial agent.